Tooth autotransplantation with adjunctive application of enamel matrix derivatives using a digital workflow: A prospective case series.

OBJECTIVES: Digital protocols and bioactive materials may reduce complications and improve tooth autotransplantation (ATT) success and survival rates. This prospective study assesses the performance of a fully digital autotransplantation protocol of close-apex molars with the adjunctive application of Enamel Matrix Derivatives (EMD). METHODS: Twelve adult patients with 13 hopeless molar teeth were replaced with autotransplantation of closed apex third molars. Outcomes, including success and survival rates, clinical, endodontic, radiographic, patient-reported outcome measures (PROMs), and digital image assessments, were conducted over a two-year follow-up period. RESULTS: Survival and success rates were 100% and 91.2%, respectively, with no progressive inflammatory or replacement root resorption (ankylosis) except for one tooth presenting radiographic furcation involvement. A significant probing depth reduction of 2.4 ± 2.58 mm and CAL gains of 2.8 ± 3.03 mm were observed in transplanted teeth compared to the hopeless receptor teeth. Radiographic bone levels remained stable throughout the study period (-0.37 ± 0.66 mm), and digital image assessments showed minimal alveolar ridge width changes (-0.32 to -0.7 mm) and gingival margin changes (-0.95 to -1.27 mm) from baseline to last visit. PROMs indicated very high patient satisfaction. CONCLUSION: The use of a digital ATT protocol with adjunctive use of EMD in closed-apex third molars demonstrated promising short-term high success and survival rates. Additionally, this type of therapy adequately preserves the dimensions of the alveolar ridge in the receptor site. CLINICAL SIGNIFICANCE: This is the first prospective clinical study examining the effect of a digital tooth autotransplantation protocol combined with the application of EMD. It demonstrates that this approach is an effective treatment for replacing hopeless teeth and also validates the digital assessment of ATT alveolar ridge preservation at the recipient site.

Recombinant human enamelin produced in Escherichia coli promotes mineralization in vitro.

BACKGROUND: Enamelin is an enamel matrix protein that plays an essential role in the formation of enamel, the most mineralized tissue in the human body. Previous studies using animal models and proteins from natural sources point to a key role of enamelin in promoting mineralization events during enamel formation. However, natural sources of enamelin are scarce and with the current study we therefore aimed to establish a simple microbial production method for recombinant human enamelin to support its use as a mineralization agent. RESULTS: In the study the 32 kDa fragment of human enamelin was successfully expressed in Escherichia coli and could be obtained using immobilized metal ion affinity chromatography purification (IMAC), dialysis, and lyophilization. This workflow resulted in a yield of approximately 10 mg enamelin per liter culture. Optimal conditions for IMAC purification were obtained using Ni2+ as the metal ion, and when including 30 mM imidazole during binding and washing steps. Furthermore, in vitro mineralization assays demonstrated that the recombinant enamelin could promote calcium phosphate mineralization at a concentration of 0.5 mg/ml. CONCLUSIONS: These findings address the scarcity of enamelin by facilitating its accessibility for further investigations into the mechanism of enamel formation and open new avenues for developing enamel-inspired mineralized biomaterials.

Clinical and Radiographic Evaluation of Intrabony Periodontal Defects Treated with Hyaluronic Acid or Enamel Matrix Proteins: A 6-Month Prospective Study.

PURPOSE: To compare the regenerative clinical and radiographic effects of cross-linked hyaluronic acid (xHyA) with enamel matrix proteins (EMD) at six months after regenerative treatment of periodontal intrabony defects. MATERIALS AND METHODS: Sixty patients presenting one intrabony defect each were randomly assigned into control (EMD) and test (xHyA) groups. Clinical attachment level (CAL) gain was the primary outcome, while pocket probing depth (PPD), gingival recession (REC), bleeding on probing (BOP), full-mouth plaque score (FMPS), full-mouth bleeding score (FMBS), and radiographic parameters such as defect depth (BC-BD), and defect width (DW) were considered secondary outcome variables. Parameters were recorded at baseline and after 6 months. RESULTS: At the 6-month follow-up, 54 patients were available for statistical analysis. In the control and test groups, the mean CAL gain was statistically significant in the intragroup comparison (p < 0.001). 48.1% of test sites showed a CAL gain ≤ 2 mm compared with 33.3% of control sites. The mean PPD reduction was statistically significant in the intragroup comparison in both groups (p < 0.001). The mean REC increase was similar in the two groups: 1.04 ± 1.29 mm vs 1.11 ± 1.22 mm (test vs control). The mean BC-BD, DW, FMPS, FMBS, and BOP changed statistically significantly only in the intragroup comparison, not in the intergroup comparison. CONCLUSION: Both treatments, EMD and xHyA, produced similar statistically significant clinical and radiographical improvements after six months when compared with baseline.

The flapless approach with and without enamel matrix derivatives for the treatment of intrabony defects: A randomized controlled clinical trial.

AIM: To compare the clinical and radiographic outcomes of flapless procedure alone or in combination with enamel matrix derivatives (EMD) in the treatment of deep intrabony defects. MATERIALS AND METHODS: Forty-six patients re-evaluated after non-surgical therapy were randomly assigned to the test (flapless with EMD) or control group (flapless alone). Clinical measurements were recorded pre-surgery and at 6 and 12 months after surgery, and radiographic measurements were taken pre-surgery and after 12 months. RESULTS: Forty-six patients completed the study. Improvements were observed in both groups at 12 months for mean clinical attachment level (CAL) gain, with significant differences between test (3.9 ± 1.1 mm) and control groups (3.0 ± 1.2) (p = .017). Probing pocket depth (PPD) reduction (4.0 ± 0.7 vs. 3.3 ± 1.4 mm) was also near to statistical significance (p = .051). Also, more sites achieved successful composite outcome measure (final PPD ≤ 4 mm and CAL gain ≥3 mm) for the regenerative treatment in the flapless + EMD group (82.6% vs. 52.2%; p = .028). In terms of radiographic outcomes, EMD yielded a greater defect bone fill than flapless treatment alone (3.0 ± 1.0 mm vs. 1.8 ± 1.5 mm; p < .001). CONCLUSIONS: The additional application of EMD during the flapless procedure for intrabony defects slightly improved clinical and radiographic outcomes. CLINICALTRIALS: gov identification number: NCT05456555.

ENAM Mutations Can Cause Hypomaturation Amelogenesis Imperfecta.

Amelogenesis imperfecta (AI) is a diverse group of inherited diseases featured by various presentations of enamel malformations that are caused by disturbances at different stages of enamel formation. While hypoplastic AI suggests a thickness defect of enamel resulting from aberrations during the secretory stage of amelogenesis, hypomaturation AI indicates a deficiency of enamel mineralization and hardness established at the maturation stage. Mutations in ENAM, which encodes the largest enamel matrix protein, enamelin, have been demonstrated to cause generalized or local hypoplastic AI. Here, we characterized 2 AI families with disparate hypoplastic and hypomaturation enamel defects and identified 2 distinct indel mutations at the same location of ENAM, c588+1del and c.588+1dup. Minigene splicing assays demonstrated that they caused frameshifts and truncation of ENAM proteins, p.Asn197Ilefs*81 and p.Asn197Glufs*25, respectively. In situ hybridization of Enam on mouse mandibular incisors confirmed its restricted expression in secretory stage ameloblasts and suggested an indirect pathogenic mechanism underlying hypomaturation AI. In silico analyses indicated that these 2 truncated ENAMs might form amyloid structures and cause protein aggregation with themselves and with wild-type protein through the added aberrant region at their C-termini. Consistently, protein secretion assays demonstrated that the truncated proteins cannot be properly secreted and impede secretion of wild-type ENAM. Moreover, compared to the wild-type, overexpression of the mutant proteins significantly increased endoplasmic reticulum stress and upregulated the expression of unfolded protein response (UPR)-related genes and TNFRSF10B, a UPR-controlled proapoptotic gene. Caspase, terminal deoxynucleotidyl transferase UTP nick-end labeling (TUNEL), and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays further revealed that both truncated proteins, especially p.Asn197Ilefs*81, induced cell apoptosis and decreased cell survival, suggesting that the 2 ENAM mutations cause AI through ameloblast cell pathology and death rather than through a simple loss of function. This study demonstrates that an ENAM mutation can lead to generalized hypomaturation enamel defects and suggests proteinopathy as a potential pathogenesis for ENAM-associated AI.

The Evaluation of Enamel Matrix Derivative on the Bone Regenerative Potential of the Dental Implant with the Transcrestal Sinus Floor Elevation Approach: A Randomized, Parallel CBCT Study.

PURPOSE: To evaluate the clinical and radiographic results of simultaneous implant placement using transcrestal sinus floor elevation (TSFE) with and without enamel matrix derivative (EMD) application. MATERIALS AND METHODS: Twenty-four patients were randomly assigned into two groups: The EMD+TSFE group (n = 13 patients, 20 implants) received TSFE with EMD application, and the TSFE group (n = 11 patients, 20 implants) received TSFE without EMD application. The patients were recalled at 3 (T3) and 12 (T12) months postsurgery. The residual bone height (RBH), implant protrusion length (IPL), peri-implant sinus bone level (SBL), endo-sinus bone gain (ESBG), and implant stability (ISQ) were measured. Multivariate regressions were performed for the groups. RESULTS: At T3, the ESBG was 3.72 ± 0.85 mm in the EMD+TSFE group and 3.10 ± 0.05 mm in the TSFE group, and there were statistically significant differences (P < .05). However, there were no statistically significant differences in ESBG at T12 between the groups (P > .05). ISQ values did not show a statistical difference between the groups at T1 and T3, but at T3 in the TSFE+EMD group, there was a statistical increase in the intragroup evaluation compared to the TSFE group. CONCLUSIONS: The use of EMD in TSFE procedures is effective in new bone formation at the apical part of the implant during the early healing period, but in the long term, no significant difference was shown between cases in which EMD was or was not used in terms of new bone formation and primary and secondary stabilization.

Ameloblastin and its multifunctionality in amelogenesis: A review.

Extracellular matrix proteins play crucial roles in the formation of mineralized tissues like bone and teeth via multifunctional mechanisms. In tooth enamel, ameloblastin (Ambn) is one such multifunctional extracellular matrix protein implicated in cell signaling and polarity, cell adhesion to the developing enamel matrix, and stabilization of prismatic enamel morphology. To provide a perspective for Ambn structure and function, we begin this review by describing dental enamel and enamel formation (amelogenesis) followed by a description of enamel extracellular matrix. We then summarize the established domains and motifs in Ambn protein, human amelogenesis imperfecta cases, and genetically engineered mouse models involving mutated or null Ambn. We subsequently delineate in silico, in vitro, and in vivo evidence for the amphipathic helix in Ambn as a proposed cell-matrix adhesive and then more recent in vitro evidence for the multitargeting domain as the basis for dynamic interactions of Ambn with itself, amelogenin, and membranes. The multitargeting domain facilitates tuning between Ambn-membrane interactions and self/co-assembly and supports a likely overall role for Ambn as a matricellular protein. We anticipate that this review will enhance the understanding of multifunctional matrix proteins by consolidating diverse mechanisms through which Ambn contributes to enamel extracellular matrix mineralization.

Genetic variations in exon 10 of ENAM and their association with early childhood caries.

OBJECTIVE: Enamelin is the largest enamel matrix protein encoded by the ENAM gene. The primary purpose of this study was to identify genetic variants in ENAM exon 10 that can alter susceptibility to early childhood caries (ECC). METHODS: This case-control study included 248 children aged 3-6 years, with 124 children diagnosed with ECC in the case group and 124 children without caries in the control group. Questionnaires were used to record demographic data, socioeconomic status, hygienic practices, and feeding practices, and a 24-h diet diary was kept. Seven polymorphisms (rs7671281, rs1738668322, rs3796703, rs3796704, rs759376039, rs775159311, and rs1738678483) in ENAM exon 10 were sequenced. RESULTS: The heterozygous CT genotype of rs7671281 was significantly more common in the case group compared to the control group (odds ratio [OR], 6.1765; 95% confidence interval [CI], 2.05-18.58; P = 0.0006). Under the dominant model, the TT genotype of rs7671281 was significantly more common in the control group (OR, 6.47; 95% CI, 2.15-19.39; P < 0.001). The AG genotype of rs3796704 was significantly more common in the case group than in the control group (OR, 5.705; 95% CI, 1.60-20.25; P = 0.006). Under the dominant model, the GG genotype of rs3796704 was significantly more common in children without caries than in children with caries (OR, 6.84; 95% CI, 1.96-23.90; P < 0.001). CONCLUSIONS: The C allele of rs7671281 and the A allele of rs3796704 can increase susceptibility to ECC.

Enamel Renal Gingival Syndrome in an Adolescent.

Enamel renal gingival syndrome is a rare clinical condition characterized by the presence of amelogenesis imperfecta hypoplastic type, gingival fibromatosis and delayed tooth eruption, in addition to nephrocalcinosis with normal blood calcium levels. It is inherited as an autosomal recessive trait caused by mutations in the FAM20A gene located on chromosome 17q24.2. The purpose of this report is to describe a case of enamel renal gingival syndrome and discuss its distinct features and management.

MiR-4319 targets tuftelin 1 to reduce malignancy of cervical cancer cells.

Cervical cancer (CC) is the most common malignant tumor of female reproductive system. MiR-4319 has been identified as an anti-oncogene in various cancers. In the present study, role of miR-4319 in CC was identified. Colony formation, flow cytometer, wound healing, and transwell assays were used to detect CC cell proliferation, apoptosis, migration, and invasion. The expression of miR-4319 was decreased in clinical CC tissues and CC cell lines. Upregulation of miR-4319 suppressed cell viability, proliferation, migration, and invasion, and induced cell apoptosis in CC cells. Moreover, tuftelin 1 (TUFT1) was verified as a direct target of miR-4319, as confirmed by dual-luciferase reporter assay. Additionally, TUFT1 expression was remarkably increased in clinical CC tissues and CC cell lines and was negatively associated with miR-4319 expression. Furthermore, overexpression of TUFT1 partially restored the effects of miR-4319 mimic on cell viability, proliferation, migration, invasion, and cell apoptosis in CC cells. To conclude, miR-4319 played an anti-cancer role in the occurrence and development of CC, which might be achieved by targeting TUFT1.

Regeneration of Rabbit Calvarial Defects with Combination of Stem Cells and Enamel Matrix Derivative: A Microcomputed Tomography and Histological Evaluation Comparing Two- and Three-Dimensional Cell Constructs.

Background and Objectives: This study addresses the challenge of bone regeneration in calvarial defects, exploring the efficacy of stem cell-based therapies and enamel matrix derivative (EMD) in tissue engineering. It assesses the regenerative potential of two- and three-dimensional cell constructs combined with mesenchymal stem cells (MSCs) and EMD in rabbit calvarial defects. Materials and Methods: This research involved the use of bone-marrow-derived MSCs cultured in silicon elastomer-based concave microwells to form spheroids. White rabbits were grouped for different treatments, with Group 1 as control, Group 2 receiving only EMD, Group 3 getting EMD plus stem cells, and Group 4 being treated with EMD plus stem cell spheroids. Computed tomography (CT) and microcomputed tomography (micro-CT) imaging were used for structural assessment, while histological evaluations were conducted using hematoxylin and eosin, Masson's trichrome, and Picro-sirius red staining. Results: CT and micro-CT analyses revealed varying degrees of bone regeneration among the groups. Group 4, treated with three-dimensional MSC spheroids and EMD, showed the most significant improvement in bone regeneration. Histological analyses corroborated these findings, with Group 4 displaying enhanced bone formation and better collagen fiber organization. Conclusions: The study supported the biocompatibility and potential efficacy of three-dimensional MSC constructs combined with EMD in bone regeneration. Further investigations are needed to confirm these findings and optimize treatment protocols.

FAM20A-Associated Amelogenesis Imperfecta: Gene Variants with Functional Verification and Histological Features.

OBJECTIVE: To investigate FAM20A gene variants and histological features of amelogenesis imperfecta and to further explore the functional impact of these variants. METHODS: Whole-exome sequencing (WES) and Sanger sequencing were used to identify pathogenic gene variants in three Chinese families with amelogenesis imperfecta. Bioinformatics analysis, in vitro histological examinations and experiments were conducted to study the functional impact of gene variants, and the histological features of enamel, keratinised oral mucosa and dental follicle. RESULTS: The authors identified two nonsense variants c. 406C > T (p.Arg136*) and c.826C > T (p.Arg176*) in a compound heterozygous state in family 1, two novel frameshift variants c.936dupC (p.Val313Argfs*67) and c.1483dupC (p.Leu495Profs*44) in a compound heterozygous state in family 2, and a novel homozygous frameshift variant c.530_531insGGTC (p.Ser178Valfs*21) in family 3. The enamel structure was abnormal, and psammomatoid calcifications were identified in both the gingival mucosa and dental follicle. The bioinformatics and subcellular localisation analyses indicated these variants to be pathogenic. The secondary and tertiary structure analysis speculated that these five variants would cause structural damage to FAM20A protein. CONCLUSION: The present results broaden the variant spectrum and clinical and histological findings of diseases associated with FAM20A, and provide useful information for future genetic counselling and functional investigation.

[Overexpression of tuftelin and KLF-5 and its clinicopathological features in hepatitis B virus-related hepatocellular carcinoma].

Objective: To analyze and evaluate the expressions and clinical value of tuftelin (TUFT1) and Krüppel-like factor 5 (KLF5) in hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) tissues. Method: KLF5 mRNA and TUFT1 mRNA transcriptional status in cancer and non-cancer groups were compared according to the Cancer Genome Atlas (TCGA) database. The differences and prognostic value between the groups were analyzed. Postoperative liver cancer and its paired pericancerous tissues, with the approval of the ethics committee, were collected to build tissue chips. The expression of KLF5 and TUFT1 and their intracellular localization were verified by immunohistochemistry. Tissue expression and clinicopathological characteristics were analyzed by immunoblotting. SPSS software was used to analyze the relationship between SPSS and patient prognosis. Results: The transcription level of TUFT1 or KLF5 mRNA was significantly higher in the HCC group than the non-cancer group (P < 0.001), according to TCGA data. Immunohistochemistry and Western blotting examination confirmed the overexpression of TUFT1 and KLF5 in human HCC tissues, which were mainly localized in the cytoplasm and cell membrane. The positivity rates of TUFT1 and KLF5 were 87.1% ( χ(2) = 18.563, P < 0.001) and 95.2% ( χ(2) = 96.435, P < 0.001) in HCC tissues, and both were significantly higher than those in the adjacent group. The expression intensity was higher in stage III-IV than stage I-II of the International Union Against Cancer standard (P < 0.01). The clinicopathological features showed that the abnormalities of the two were significantly related to HBV infection, tumor size, extrahepatic metastasis, TNM stage, and ascites. Univariate analysis was related to tumor size, HBV infection, and survival. Multivariate analysis was an independent prognostic factor for patients with HCC. Conclusion: TUFT1 and KLF5 may both be novel markers possessing clinical value in the diagnosis and prognosis of HBV-related HCC.

FAM20A is a golgi-localized Type II transmembrane protein.

Family with sequence similarity 20, member A (FAM20A) is a pseudo-kinase in the secretory pathway and is essential for enamel formation in humans. Here we examine if FAM20A is a membrane-associated protein. We show that the full-length FAM20A can be purified from HEK293 cells transfected with a FAM20A-expresing construct. Further, it is only found in the membrane fraction, but not in the soluble fraction, of cell lysate. Consistently, it is not secreted out of the expressing cells. Moreover, it is co-localized with GM130, a cis-Golgi network marker, and membrane topology analysis indicates that it has its C-terminus oriented towards the lumen of the organelle. Our results support that FAM20A is a Type II transmembrane protein within the secretory compartments.

In-depth investigation of FAM20A insufficiency effects on deciduous dental pulp cells: Altered behaviours, osteogenic differentiation, and inflammatory gene expression.

AIM: Loss-of-function mutations in FAM20A result in amelogenesis imperfecta IG (AI1G) or enamel-renal syndrome, characterized by hypoplastic enamel, ectopic calcification, and gingival hyperplasia, with some cases reporting spontaneous tooth infection. Despite previous reports on the consequence of FAM20A reduction in gingival fibroblasts and transcriptome analyses of AI1G pulp tissues, suggesting its involvement in mineralization and infection, its role in deciduous dental pulp cells (DDP) remains unreported. The aim of this study was to evaluate the properties of DDP obtained from an AI1G patient, providing additional insights into the effects of FAM20A on the mineralization of DDP. METHODOLOGY: DDP were obtained from a FAM20A-AI1G patient (mutant cells) and three healthy individuals. Cellular behaviours were examined using flow cytometry, MTT, attachment and spreading, colony formation, and wound healing assays. Osteogenic induction was applied to DDP, followed by alizarin red S staining to assess their osteogenic differentiation. The expression of FAM20A-related genes, osteogenic genes, and inflammatory genes was analysed using real-time PCR, Western blot, and/or immunolocalization. Additionally, STRING analysis was performed to predict potential protein-protein interaction networks. RESULTS: The mutant cells exhibited a significant reduction in FAM20A mRNA and protein levels, as well as proliferation, migration, attachment, and colony formation. However, normal FAM20A subcellular localization was maintained. Additionally, osteogenic/odontogenic genes, OSX, OPN, RUNX2, BSP, and DSPP, were downregulated, along with upregulated ALP. STRING analysis suggested a potential correlation between FAM20A and these osteogenic genes. After osteogenic induction, the mutant cells demonstrated reduced mineral deposition and dysregulated expression of osteogenic genes. Remarkably, FAM20A, FAM20C, RUNX2, OPN, and OSX were significantly upregulated in the mutant cells, whilst ALP, and OCN was downregulated. Furthermore, the mutant cells exhibited a significant increase in inflammatory gene expression, that is, IL-1ß and TGF-ß1, whereas IL-6 and NFκB1 expression was significantly reduced. CONCLUSION: The reduction of FAM20A in mutant DDP is associated with various cellular deficiencies, including delayed proliferation, attachment, spreading, and migration as well as altered osteogenic and inflammatory responses. These findings provide novel insights into the biology of FAM20A in dental pulp cells and shed light on the molecular mechanisms underlying AI1G pathology.

Co-exposure to fluoride and sulfur dioxide induces abnormal enamel mineralization in rats via the FGF9-mediated MAPK signaling pathway.

Fluoride (F) and sulfur dioxide (SO2) contamination is recognized as a public health concern worldwide. Our previous research has shown that Co-exposure to F and SO2 can cause abnormal enamel mineralization. Ameloblastin (AMBN) plays a crucial role in the process of enamel mineralization. However, the process by which simultaneous exposure to F and SO2 influences enamel formation by regulating AMBN expression still needs to be understood. This study aimed to establish in vivo and in vitro models of F-SO2 Co-exposure and investigate the relationship between AMBN and abnormal enamel mineralization. By overexpressing/knocking out the Fibroblast Growth Factor 9 (FGF9) gene, we investigated the impact of FGF9-mediated Mitogen-Activated Protein Kinase (MAPK) signaling on AMBN synthesis to elucidate the mechanism underlying the induction of abnormal enamel mineralization by F-SO2 Co-exposure in rats. The results showed that F-SO2 exposure damaged the structure of rat enamel and ameloblasts. When exposed to F or SO2, gradual increases in the protein expression of FGF9 and phosphorylated p38 mitogen-activated protein kinase (p-P38) were observed. Conversely, the protein levels of AMBN, phosphorylated extracellular signal-regulated kinase (p-ERK), and phosphorylated c-Jun N-terminal kinase (p-JNK) were decreased. AMBN expression was significantly correlated with FGF9, p-ERK, and p-JNK expression in ameloblasts. Interestingly, FGF9 overexpression reduced the levels of p-ERK and p-JNK, worsening the inhibitory effect of F-SO2 on AMBN. Conversely, FGF9 knockout increased the phosphorylation of ERK and JNK, partially reversing the F-SO2-induced downregulation of AMBN. Taken together, these findings strongly demonstrate that FGF9 plays a critical role in F-SO2-induced abnormal enamel mineralization by regulating AMBN synthesis through the JNK and ERK pathways.

Epigenetic Regulation of Ameloblast Differentiation by HMGN Proteins.

Dental enamel formation is coordinated by ameloblast differentiation, production of enamel matrix proteins, and crystal growth. The factors regulating ameloblast differentiation are not fully understood. Here we show that the high mobility group N (HMGN) nucleosomal binding proteins modulate the rate of ameloblast differentiation and enamel formation. We found that HMGN1 and HMGN2 proteins are downregulated during mouse ameloblast differentiation. Genetically altered mice lacking HMGN1 and HMGN2 proteins show faster ameloblast differentiation and a higher rate of enamel deposition in mice molars and incisors. In vitro differentiation of induced pluripotent stem cells to dental epithelium cells showed that HMGN proteins modulate the expression and chromatin accessibility of ameloblast-specific genes and affect the binding of transcription factors epiprofin and PITX2 to ameloblast-specific genes. Our results suggest that HMGN proteins regulate ameloblast differentiation and enamel mineralization by modulating lineage-specific chromatin accessibility and transcription factor binding to ameloblast regulatory sites.

ASH2L, Core Subunit of H3K4 Methylation Complex, Regulates Amelogenesis.

Histone methylation assumes a crucial role in the intricate process of enamel development. Our study has illuminated the substantial prevalence of H3K4me3 distribution, spanning from the cap stage to the late bell stage of dental germs. In order to delve into the role of H3K4me3 modification in amelogenesis and unravel the underlying mechanisms, we performed a conditional knockout of Ash2l, a core subunit essential for the establishment of H3K4me3 within the dental epithelium of mice. The absence of Ash2l resulted in reduced H3K4me3 modification, subsequently leading to abnormal morphology of dental germ at the late bell stage. Notably, knockout of Ash2l resulted in a loss of polarity in ameloblasts and odontoblasts. The proliferation and apoptosis of the inner enamel epithelium cells underwent dysregulation. Moreover, there was a notable reduction in the expression of matrix-related genes, Amelx and Dspp, accompanied with impaired enamel and dentin formation. Cut&Tag-seq (cleavage under targets and tagmentation sequencing) analysis substantiated a reduction of H3K4me3 modification on Shh, Trp63, Sp6, and others in the dental epithelium of Ash2l knockout mice. Validation through real-time polymerase chain reaction, immunohistochemistry, and immunofluorescence consistently affirmed the observed downregulation of Shh and Sp6 in the dental epithelium following Ash2l knockout. Intriguingly, the expression of Trp63 isomers, DNp63 and TAp63, was perturbed in Ash2l defect dental epithelium. Furthermore, the downstream target of TAp63, P21, exhibited aberrant expression within the cervical loop of mandibular first molars and incisors. Collectively, our findings suggest that ASH2L orchestrates the regulation of crucial amelogenesis-associated genes, such as Shh, Trp63, and others, by modulating H3K4me3 modification. Loss of ASH2L and H3K4me3 can lead to aberrant differentiation, proliferation, and apoptosis of the dental epithelium by affecting the expression of Shh, Trp63, and others genes, thereby contributing to the defects of amelogenesis.

Novel Ameloblastin Variants, Contrasting Amelogenesis Imperfecta Phenotypes.

Amelogenesis imperfecta (AI) comprises a group of rare, inherited disorders with abnormal enamel formation. Ameloblastin (AMBN), the second most abundant enamel matrix protein (EMP), plays a critical role in amelogenesis. Pathogenic biallelic loss-of-function AMBN variants are known to cause recessive hypoplastic AI. A report of a family with dominant hypoplastic AI attributed to AMBN missense change p.Pro357Ser, together with data from animal models, suggests that the consequences of AMBN variants in human AI remain incompletely characterized. Here we describe 5 new pathogenic AMBN variants in 11 individuals with AI. These fall within 3 groups by phenotype. Group 1, consisting of 6 families biallelic for combinations of 4 different variants, have yellow hypoplastic AI with poor-quality enamel, consistent with previous reports. Group 2, with 2 families, appears monoallelic for a variant shared with group 1 and has hypomaturation AI of near-normal enamel volume with pitting. Group 3 includes 3 families, all monoallelic for a fifth variant, which are affected by white hypoplastic AI with a thin intact enamel layer. Three variants, c.209C>G; p.(Ser70*) (groups 1 and 2), c.295T>C; p.(Tyr99His) (group 1), and c.76G>A; p.(Ala26Thr) (group 3) were identified in multiple families. Long-read AMBN locus sequencing revealed these variants are on the same conserved haplotype, implying they originate from a common ancestor. Data presented therefore provide further support for possible dominant as well as recessive inheritance for AMBN-related AI and for multiple contrasting phenotypes. In conclusion, our findings suggest pathogenic AMBN variants have a more complex impact on human AI than previously reported.

Deep dental phenotyping and a novel FAM20A variant in patients with amelogenesis imperfecta type IG.

OBJECTIVES: To identify etiologic variants and perform deep dental phenotyping in patients with amelogenesis imperfecta (AI). METHODS: Three patients of two unrelated families were evaluated. Genetic variants were investigated by exome and Sanger sequencing. An unerupted permanent third molar (AI1) from Patient1 and a deciduous first molar (AI2) from Patient2, along with three tooth-type matched controls for each were characterized. RESULTS: All three patients harbored biallelic pathogenic variants in FAM20A, indicating AI1G. Of the four identified variants, one, c.1231C > T p.(Arg411Trp), was novel. Patient1 possessed the largest deletion, 7531 bp, ever identified in FAM20A. In addition to hypoplastic enamel, multiple impacted teeth, intrapulpal calcification, pericoronal radiolucencies, malocclusion, and periodontal infections were found in all three patients, gingival hyperplasia in Patient1 and Patient2, and alveolar bone exostosis in Patient3. Surface roughness was increased in AI1 but decreased in AI2. Decreased enamel mineral density, hardness, and elastic modulus were observed in AI1 enamel and dentin and AI2 dentin, along with decreased phosphorus, increased carbon, and increased calcium/phosphorus and carbon/oxygen ratios. Severely collapsed enamel rods and disorganized dentin-enamel junction were observed. CONCLUSIONS: We report a novel FAM20A variant and, for the first time, the defective mineral composition and physical/mechanical properties of AI1G teeth.